A rotary shaver with slidably mounted blades

ABSTRACT

A cutting blade which can be slidably mounted in a slot in the motor-driven shaft of an electric shaver. The cutting blade is weighted a precise amount to thereby control the magnitude of the pressure with which the cutting edge of the blade engages the comb of the razor.

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A ROTARY SHAVER WITH SLIDABLY MOUNTED BLADES DESCRIPTION OF THE PRIOR ART Electric razors are commercially available in a plurality of types and sizes at the present time each having various types of blade and comb constructions. Generally, the methods employed in these razors for holding the blade in engagement with the comb fall into two categories, those which use complex mechanisms such as shaft gearing and/or spring arrangements or those which rely on centrifugal force. None of these methods have proven to be entirely satisfactory. Complex gearing and spring arrangements greatly increase the cost of the completed shaver and are very susceptible to jamming and breakage of parts, whereas those shavers which employ centrifugal force experience excessive blade and comb wear requiring frequent replacement of these parts.

The present invention eliminates the aforementioned disadvantages of present-day electric shavers by providing an electric shaver which is uncomplicated in its construction, relatively inexpensive in its cost to manufacture and which, because of its unique blade design, there results a greatly increased useful life of both the blade and the comb.

SUMMARY OF THE INVENTION The shaver of the present invention employs a constant speed electric motor which has a slotted shaft on one end thereof. The slot is of sufficient width to receive two identical cutter blades and permit the blades to slidably engage each other as well as the sides ofthe slot. The axial movement of the blades is limited by screws in the end of the shaft. The blades themselves are rectangular in shape and have a cutting edge ex tending along one end thereof. A groove is formed in the blade to limit its movement in the slot in the radial direction. Each of the blades has a weighted portion, the mass of which from the center of rotation of the shaft is chosen to be a specific amount less than the mass of the portion of the blade which extends from the center of rotation of the shaft having the cutting edge. The relative masses of the two portions are so chosen that as the blades are rotated at a constant velocity, the cutting edge will contact the inside surface of a cylindrical-shaped comb with a force just sufficient to effectively cut whiskers or hair extending through apertures in the comb in the path of the rotating cutting edge. By limiting the centrifugal force and, thus, the pressure exerted by the cutting edge against the inside surface of the comb in this manner, the useful life of both the cut ting edge and comb are greatly extended. In addition, when the blades eventually do need replacing, their unique design and the means by which they hold in the slot on the shaft greatly-facilitate their removal and replacement by the average user.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of an electric shaver having a portion broken away to show the interior construction.

FIG. 2 is an enlarged cross-sectional view of the shaving blades of one embodiment of the electric shaver taken along lines 22 of FIG. 1.

FIG. 3 is an enlarged cross-sectional view of the shaving blades of another embodiment of the electric shaver.

FIG. 4 is a partial perspective view of the cutting blades and comb of the present invention.

FIG. 5 is a partial perspective view of a blade having a counterbalancing weighted portion.

FIG. 6 is a partial perspective view of another blade without a counterbalancing portion.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings where like numerals indicate like elements, FIG. 1 shows an electric shaver 10 having a housing 12 within which is mounted an electric motor 14. The electric motor has a drive shaft 16 which is rotated at speeds of between 10 and 15,000 revolutions per minute. A flexible electric cord 18 is shown for supplying electric current to the motor 14.

The drive shaft 16 is rotatably mounted in a sleeve bearing 20 formed in one end 22 of the housing 12. The drive shaft 16 also has a slotted shaft 4 connected to or formed integrally with it for holding a pair of cutting blades in a manner to be described later.

A tubular comb or guard 26 is removably mounted on the end 22 of the housing 12 by means of threads 28 formed on the end 22 and the comb 26. The comb 26 has an inside cylindrical surface 30 concentric with the center of the slotted shaft 24 and an outside surface 32. A plurality of perforations or hair holes 34 extend through the comb 26.

In the embodiment of the invention shown in FIGS. 2, 4 and 5, a cutting blade 36 has a first portion 38 and a second portion 40. The first portion 38 extends a radial distance a from the center of rotation of the slotted shaft 24 to a cutting edge 42 when the blade 36 contacts the inside surface 30 and a second or weighted portion 40 extends a radial distance b from the center of rotation of the slotted shaft 24 when the cutting edge 42 contacts the inside surface 30 as shown in FIG. 2. The cutting edge 42 extends the length of the first portion 38.

The cutting blade also has a three-sided recess 44 extending parallel to the cutting edge 42, the surface 46 of recess 44 has a first side 48 and a second side 50. The slotted shaft 24 can have either a rounded outer surface 52 or a flat outer surface 54 as shown in FIGS. 2 and 3, respectively, for use with the blades of either embodiment of the invention.

The blades 36 are positioned in the slotted shaft 24 having opposite slot faces 56 such that the surface 46 of each of theblades 36 is in engagement with one of the slot faces 56. The first side 48 and second side 50 of recesses 44 serve to prevent the blades 36 from being removed in a radial direction whenever the comb 26 is removed during cleaning. Screws 57 have heads which prevent axial movement of the blades 36 during use but which do not prevent radial movement of the blades with respect to each other or the shaft 24. Whenever the blades 36 become dull, the screws 57 can be easily removed by the user and the old blades lifted out to be either resharpened or replaced entirely.

In this embodiment of the invention, as the slotted shaft 24 rotates at high speed, the blades 36 are held in contact with the inside surface 30 by means of centrifugal force. The amount of pressure with which the cutting edge 42 engages the inside surface 30 of the comb 26 is equal to the centrifugal force exerted by the cutting blade 36 divided by the surface area of the cutting edge 42. In conventional electric shavers which rely on centrifugal force to hold the cutting blade in engagement with the inside surface of the comb, the aforementioned pressure is many times greater than the actual amount of pressure necessary to insure efficient cutting of hair extending through the comb in the path of the blade. This excessive pressure in conventional shavers results in very rapid dulling of the cutting'edge of the blade and general deterioration of the comb. Efficient cutting in electric shavers is primarily due to the sharpness of the cutting edge as well as the rapid movement of the blade and to a much lesser extent to the amount of pressure with which the cutting edge engages the inside surface of the comb.

To thereby reduce the pressure and, thus, extend the life of the cutting edge as well as the comb, applicant has devised a unique and novel way of reducing the centrifugal force and, thus, the pressure to an amount just sufficient to effectively cut hair extending through apertures 34 in the path of the cutting edge 42.

The foregoing relationships can be more clearly understood by reference to the following equation: P F/A, where P is the pressure in pounds per square inch, F in the centrifugal force in pounds exerted by the blade against the inside surface of the comb and A is the area in square inches of the cutting edge of the blade in contact with the inside surface of the comb. Further, the centrifugal force F can be represented by the following equation: F MV /32R where M is the mass in pounds of the blade extending from the center of rotation of the slotted shaft holding the blades, V equals the velocity in feet per second at which the cutting edge of the blade rotates, and R is the distance in feet from the center of rotation of the slotted shaft to the inside surface of the comb. The constant (32) is the force of gravity in feet/sec? When the two foregoing equations are combined to form the equation P MV /32 RA, it can readily be seen that, as in conventional shavers, for a constant mass M and constant radius R, a high velocity V and a very small area A will result in a very high pressure P.

The unique design of applicants cutting blade 36 considerably reduces the pressure P which, as previously stated, results in an increase in both the useful life of the blade cutting edge 42 as well as the comb 26.

This reduction in the pressure P, to an amount just sufficient to insure the efficient cutting of hair extending through the perforations 34, is accomplished by reducing the centrifugal force exerted by the portion 38 of the cutting blade 36 in the direction of the cutting edge 42 by means of a counterbalancing centrifugal force exerted in a direction away from the cutting edge 42 which is provided by the weighted portion 40 located on the portion of the cutting blade 36 opposite the cutting edge 42.

The resultant force (F can be represented by the equation: F 1/32 (V Ml/a V M2/b) where a is the distance in feet from the center of rotation of the slotted shaft 24 to the cutting edge 42, M is the mass of pounds of the first portion 38 which extends a distance a from the center of rotation of the slotted shaft 24 to the cutting edge 42, b is the distance in feet from the center of rotation of the slotted shaft 24 to the cutting blade surface 58 and M is the mass in pounds of the second portion 40 which extends a distance b from the center of rotation of the slotted shaft 24 to the cutting blade surface 58. V is the velocity in feet per second at which the cutting edge 42 rotates at a distance a and V is the velocity in feet per second at which the cutting blade surface 58 rotates at a distance b. (The foregoing distances a and b and the respective masses M and M are determined when the cutting edge 42 is in contact with the inner surface 30 of the comb 26 as shown in FIG. 2.)

The mass M and distance b of the second portion 40 are, thus, so chosen that the counterbalancing centrifugal force exerted thereby will reduce the centrifugal force and therefore pressure exerted by the first portion 38 at the point where the cutting edge 42 engages the inside surface of the comb 26 to an amount just sufficient for effective cutting of hair extending through perforations 34 in the path the cutting edge 42. In this embodiment, the sides 48 and 50 of the recess 44 do not contact the outside surface 52 when the cutting edge 42 is in contact with the inside surface 30 of the comb 26.

The second embodiment of the invention shown in FlGS. 3 and 6 does not employ applicants novel counterbalancing weighted portion 40. The cutting blade has a cutting edge 42 and a three-sided recess 44 having a surface 46 and first and second sides 48, 50, respectively, as does the cutting blade 36. When the blade 60 is in position on the slotted shaft 24, the first and second sides 48, 50 prevent radial movement of the cutting blades out of the slotted shaft 24 whenever the comb 26 is removed for cleaning. However, in this embodiment when the cutting blade 60 is rotating, the distance c from the first side 48 to the cutting edge 42 is the same as the perpendicular distance from the'flat outer surface 54 through the center of rotation of the slotted shaft 24 to the inside surface 30 of the comb 26. As the cutting blade 60 rotates, the first side 48 engages the flat outer surface 54 to permit the cutting edge 42 to just engage the inside surface 30. By so limiting the travel of the cutting blade 60, sufficient but not excessive pressure can be maintained by the cutting edge 42 on the inside surface 30 to efficiently cut hair extending through perforations 34 into the path of the cutting edge 42. Also, when the inside surface 30 engages the flat outer surface 54 and is held there by centrifugal force, the cutting edge 42 will remain parallel to and in contact with the inside surface 30 throughout its length.

It is, of course, understood that the slotted shaft 24 having either a rounded outer surface 52 or flat outer surface 54 can be used for either embodiment of the invention.

What I claim is:

l. A shaving device comprising:

a. a housing,

b. an electric motor mounted within said housing and having a rotatable shaft extending from one end of said housing, said shaft having a slot through the center of rotation of said shaft and extending substantially the length of said shaft, said slot having (two) opposed surfaces, each of said surfaces terminating at the outer surface of said shaft,

c. a comb mounted on said housing and having a plurality of aperatures therein, and

d. oppositely disposed cutter blades mounted in said slot for movement relative to each other and transverse to said center of rotation, each of said blades being of single piece construction extending substantially the length of said slot and having a three sided recess, said recess extending substantially the length of said blades such that when said blades are positioned in said slot one side of each of said recesses is in contact with one of said opposed surfaces. 1

2. The shaving device of claim 1 wherein another of said sides of each of said recesses engages said outer surface of said shaft to thereby limit movement of said blades when said shaft is rotating.

3. The shaving device of claim 1 wherein another of said sides of each of said recesses engages said outer surface of said shaft to thereby limit movement of said blades when said shaft is not rotating.

4. The shaving device of claim 2 wherein the remaining side of each of said recesses engages said outer surface of said shaft to thereby limit movement of said blades when said shaft is not rotating.

5. A shaving device comprising:

a. a housing,

b. an electric motor mounted within said housing and having a rotatable shaft extending from one end of said housing, said shaft having a slot through the center of rotation of said shaft and extending substantially the length of said shaft,

c. a comb mounted on said housing having a plurality of apertures therein, and

d. oppositely disposed cutter blades mounted in said slot for movement relative to each other and transverse to said center of rotation, each of said blades being of single piece constructionextending substantially the length of said slot and having a first and second portion, said first and second portions having masses relative to each other such that the force exerted by each of said blades against said comb as said shaft rotates is not more than the amount rquired to cut a plurality of hairs extending through said apertures.

6. The shaving device of claim 5 wherein said first portion of each of said blades extends from said center of rotation to a cutting edge on said blade when said cutting edge is in contact with said comb. 

1. A shaving device comprising: a. a housing, b. an electric motor mounted within said housing and having a rotatable shaft extending from one end of said housing, said shaft having a slot through the center of rotation of said shaft and extending substantially the length of said shaft, said slot having (two) opposed surfaces, each of said surfaces terminating at the outer surface of said shaft, c. a comb mounted on said housing and having a plurality of aperatures therein, and d. oppositely disposed cutter blades mounted in said slot for movement relative to each other and transverse to said center of rotation, each of said blades being of single piece construction extending substantially the length of said slot and having a three sided recess, said recess extending substantially the length of said blades such that when said blades are positioned in said slot one side of each of said recesses is in contact with one of said opposed surfaces.
 2. The shaving device of claim 1 wherein another of said sides of each of said recesses engages said outer surface of said shaft to thereby limit movement of said blades when said shaft is rotating.
 3. The shaving device of claim 1 wherein another of said sides of each of said recesses engages said outer surface of said shaft to thereby limit movement of said blades when said shaft is not rotating.
 4. The shaving device of claim 2 wherein the remaining side of each of said recesses engages said outer surface of said shaft to thereby limit movement of said blades when said shaft is not rotating.
 5. A shaving device comprising: a. a housing, b. an electric motor mounted within said housing and having a rotatable shaft extending from one end of said housing, said shaft having a slot through the center of rotation of said shaft and extending substantially the length of said shaft, c. a comb mounted on said housing having a plurality of apertures therein, and d. oppositely disposed cutter blades mounted in said slot for movement relative to each other and transverse to said center of rotation, each of said blades being of single piece construction extending substantially the length of said slot and having a first and second portion, said first and second portions having masses relative to each other such that the force exerted by each of said blades against said comb as said shaft rotates is not more than the amount rquired to cut a plurality of hairs extending through said apertures.
 6. The shaving device of claim 5 wherein said first portion of each of said blades extends from said center of rotation to a cutting edge on said blade when said cutting edge is in contact with said comb. 